Drilling out Holley NH passages questions...

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Model T Ford Forum: Forum 2012: Drilling out Holley NH passages questions...
Top of pagePrevious messageNext messageBottom of page Link to this message  By Marshall V. Daut on Sunday, October 07, 2012 - 07:31 pm:

I already searched the archives for the answer to these questions. Even though there are many excellent and informative postings about the NH, I couldn't seem to find one that specifically addressed my questions. It's probably there, but I just didn't see it. So, I'll ask here and now.
I am about to drill out the three brass-plugged passages on a '25-27 Holley NH carburetor. (The fourth hole is already open beneath the name plate.) I have a couple color photos that were posted here, which show the passageways drilled out and straws or pipe cleaners sticking out of the holes. These are most helpful, but my questions precede cramming pipe cleaners into the opened passageways:
(1) What size drill bit should be used to drill out the brass plugs and then through the passages?
(2) Does drilling the passageways oversized adversely affect performance? In other words, is there a perfect-sized drill bit to use that will take out the brass plugs and adequately clean out the passageways?
(3) How far does one drill? Until firm metal (the carb body) is reached, such as a dead end or an intersection with another passageway? Is there a specified depth for each hole's drilling? I don't want to drill too far and mistakenly extend the original passageways, possibly going through the carb body!
(4) I plan to fill the holes with small allen head plugs after tapping them. Or is there a better way?
I have the MTFCA carb book, but it's a little skimpy on information when discussing these points. Providing passageway locations, drill bit sizes and suggested drilling depths would have been helpful. I can't be the first person to request this information - can I?
Thanks in advance.
Marshall


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill dugger on Sunday, October 07, 2012 - 08:14 pm:

Why drill the passages? Why If it has been boiled in carb cleaner, and all is open install the kit and go for it. It is going to work or it is not going to workm . I made a small coffee can test stand so as to check the float.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Dupree on Sunday, October 07, 2012 - 08:17 pm:

My practice-

1. The plugs themselves are 1/8 inch od, and about 3/16 deep. If anything, I would drill them slightly undersize, with the expectation that the rest of the plug will come out as you are drilling.

2. Do not drill the passages oversize. You will be affecting the idle fuel/air ratio significantly. You are trying to clean the rust and crud out of the passages. Find a drill that is slightly smaller than the passage. I have a small chuck that was intended to be inserted into a nut driver. I typically use that chuck to hold the bit and turn the chuck with my fingers. This is NOT a spot where you want to break a bit.
3. Drill until you bottom out. That is why it is nice to rotate the drill by hand. When you are done drilling, blow out the passage with air to insure that the passage is open.
4. Allen plugs are probably too big. Look for 1/8 inch od brazing rod (may be hard to find) or 1/8 inch od round brass bar stock. Easy to cut to length and peen into place like the original was done.

Ron Dupree


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, October 07, 2012 - 08:45 pm:

Drill em out with a #29 (.136) drill and tap them 8/32. Install Allen set screws for plugs. Works ever time. Makes it easy to pull the plug and clean the passages again. Nobody will ever notice that there are modern Allen head plugs instead of brass. They will stay in, they will not leak and you can do it once and do it right.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, October 07, 2012 - 08:46 pm:

If you go back far enough in the posts, you will find some pictures I posted of doing this.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, October 07, 2012 - 08:50 pm:

One good use for WD40, use the small straw and blow it through the passages first to see if you even need to drill the plugs out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Marshall V. Daut on Sunday, October 07, 2012 - 09:12 pm:

Hi, Stan -
The Allen screws also appealed to me for future cleaning, but I was unable to find your photo post among the hundreds I looked through, turned up by the search engine. Are the photos or the exact thread handy to re-post? It might also help someone else out there, who's as clueless as I am in this area.
Thanks.
Marshall


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Sunday, October 07, 2012 - 10:18 pm:

I like Stan's method of cleaning out passages with a brass-wound guitar string. Rough enough to knock loose the crud and soft enough not to damage the passages.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Sunday, October 07, 2012 - 10:30 pm:

Here is the photo of Stan's set screw plug:
http://www.mtfca.com/discus/messages/118802/151382.html?1279536155
Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Sunday, October 07, 2012 - 10:31 pm:

Steve, what note do you tune the string to? Can it play Classical Gas then?? Inquiring minds want to know.

Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Sunday, October 07, 2012 - 10:36 pm:

If you're cleaning a Holley, use a G string.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Monday, October 08, 2012 - 12:43 am:

From my experience, I usually don't drill out the passages to clean them. I spray carb cleaner in them until it comes out clean by the needle and seat, and every carb that I've worked on has run fantastically.

Now if the carb cleaner doesn't come out indicating that the passages are completely blocked, then I drill out the plugs and clean the passages.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Clipner-Los Angeles on Monday, October 08, 2012 - 01:44 am:

I was looking for the same info last week. I ended up soaking in carb cleaner and brushing out the best i could. Rinsed and and kept skirting cleaner thru passages with straw. Squirting one way them back the opposite direction best that could do. Must have worked, carb working great.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Huson, Berthoud, Co. on Monday, October 08, 2012 - 10:40 am:

Marshal Daut:

Be very careful when you plug the middle plug. It is VERY, VERY easy to BREAK OUT the shoulder.

waiting to be installed


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Huson, Berthoud, Co. on Monday, October 08, 2012 - 10:42 am:

I will try the picture again.

waiting to be installed


Top of pagePrevious messageNext messageBottom of page Link to this message  By Marshall V. Daut on Monday, October 08, 2012 - 10:51 am:

Dave Huson -
Thanks for the advisory. The "middle plug" being.....?
I believe there are three brass plugs to drill out, correct? One on the manifold flange, one on the outside near the air vent hole (beneath the patent plate) and one on the underside near the top of the "stem".
Marshall


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Monday, October 08, 2012 - 10:59 am:

Steve, I wouldn't want my G string to get that gas smell. They are so hard to wash.......

Seriously, I like the 8/32 set screw idea and will use that next time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, October 08, 2012 - 12:47 pm:

Marshall,

I believe the hole under the patent plate is supposed to be open. It's the vent hole for the bowl and allows air to pass through as the fuel level rises and falls in the bowl.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Marshall V. Daut on Monday, October 08, 2012 - 01:26 pm:

Jerry -
You are correct. But there is a brass plug nearby that needs to be drilled out in order to clean out that passageway. The air vent hole stays open beneath the patent plate, but still gets cleaned.
Thanks to all, who have replied with suggestions and advice. Success might just be at hand after all.
Marshall


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Monday, October 08, 2012 - 01:53 pm:

If you are worried about getting the hole centered to drill them out just throw it in your powder coating oven after you bead blast it and heat it up to about 400 degrees and let it cool down to where it is just a little too hot to handle without a glove. The brass plugs will pop right out as soon as the drill bit starts to bite into them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Vaughn on Monday, October 08, 2012 - 04:18 pm:

Here is a picture that was posted on the forum a couple of years ago. It is a good shot of the passageways after they have been cleaned. As Stan has said this is not that difficult to do just take your time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Marshall V. Daut on Monday, October 08, 2012 - 06:11 pm:

Thanks, guys. I just finished drilling out the plugs with the #29 drill bit, as recommended. I used a smaller bit for cleaning out the passageways, which were REALLY plugged! It took the drill and bit to finally break up the congealed crud inside. At first I thought I had hit the carb body itself, but as the bit turned, more and more crud came out. I blew compressed air through all the holes and got results from the other holes. It must have worked!
The 8/32" tap and Allen head set plugs sealed up everything very nicely. I'm certain that simply soaking the carb top in cleaner would not have loosened up these passageways. It never does with Model A carbs that I have attempted to clean out this way. I like the physical cleaning idea better. It's more certain.
Great advice, Guys! Thanks again.
Marshall


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Monday, October 08, 2012 - 06:30 pm:

Glad it worked, Marshall. In my experience, which now runs to about 500 old carburetors, all carb cleaner does is loosen the crap up so it will plug something up when it gets gasoline in it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Huson, Berthoud, Co. on Tuesday, October 09, 2012 - 01:23 am:

I will try the picture again.

waiting to be installed


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